1. Field of the Invention
The present invention relates a projection zoom lens of a 6-group configuration and 4-group movement mounted on a projection type display device or the like and a projection type display device having the projection zoom lens, and more particularly, to a projection zoom lens and a projection type display device suitable for projecting on the large screen in a movie theater or the like.
2. Description of Related Art
A projector device (projection type display device) having a relatively long back focal length using a light valve such as a liquid crystal display and a DMD display has come into wide use (see JP-A-8-201690).
Recently, in movie theaters, a projector that is suitable for a large screen and is capable of projecting a higher-precision picture has been used as such a projector device.
A reflection type liquid crystal display element or a DMD 3-sheet type is used for the projector device provided for such a use, and a longer back focal length and telecentricity as satisfactory as the other projectors are necessary.
In a projection zoom lens of such a projector device, when a focus group located on a magnification side is configured to have a positive refractive power and an angle of view is widened, a lens diameter of the magnification side becomes too large. Accordingly, in a point of view of widening the angle of view, it is preferable that the focus group located on the magnification side is configured to have a negative refractive power.
However, when the focus group located on the magnification side is configured to have a negative refractive power, it is difficult to keep Fno constant as increasing a zoom ratio.
In such a case, it is important to keep Fno constant by providing an aperture diaphragm, in the zoom lens group.
As a zoom lens, in which a focus group located on a magnification side has a negative refractive power and an aperture diaphragm is provided in a zoom lens group, there is a zoom lens described in JP-A-2008-46259 and JP-A-2008-83229.
In the zoom lens described in JP-A-2008-46259, an aperture diaphragm is provided in a movement group to keep Fno substantially constant. However, in this case, it is necessary to largely change a diameter of the aperture diaphragm, and thus it is complicated to operate the aperture diaphragm.
In the zoom lens described in JP-A-2008-83229, an aperture diaphragm is moved independently from lenses during zooming. However, a diameter of the aperture diaphragm is not changed, and thus Fno is changed during zooming.